This invention relates to imaging a completion string in a wellbore.
The geometry and orientation of the wellbore and how a completion string sits in the wellbore play a large role in determining the effectiveness of the completion during clean up, treatment, cementing/isolation, and production. Typically, a wellbore extending through a formation is not straight, but rather extends in a snake-like fashion through the formation. Such wellbores typically are spiral-shaped, which results from the rotary motion of the drill bit as the well is drilled.
Even wells which are considered "straight" have variations in deviation and direction. While these variances may be small, they can have an effect, as the clearances between the wellbore walls and the completion string or casing may be quite small. For example, an 81/2" inside diameter borehole will often have a 7" outside diameter casing set inside it. This leaves only 3/4 clearance on each side.
Problems associated with the unpredictable shape of the wellbore are more pronounced in highly deviated or horizontal wells, which are widely used currently to enhance reservoir production. It may sometimes be difficult to place a completion string, such as a casing, into the wellbore without damaging the completion string. The completion string is not always damaged, but in many cases production is affected or is not optimal.
Logging and imaging tools exist that determine the shape of the wellbore. One such logging tool is a dipmeter, which includes sensors to measure the variations of formation conductivity as the dipmeter passes through the wellbore. Further, the dipmeter has calipers that measure the size of the wellbore continuously, as well as other sensors to measure the deviation and direction of the well. Based on the recorded data, a three-dimensional image along with its position can be created of the wellbore. Other types of instruments can be used to obtain the needed geometric information. For example, a borehole geometry tool (BGT) is basically a dipmeter minus the sensors for taking conductivity measurements. An ultrasonic borehole imaging (UBI) tool works with a general purpose inclinometry tool (GPIT) to obtain the image and position of the well.
The physical characteristics of the geologic formations in the well as well as the amounts and locations of the hydrocarbons in the formation are determined by other logging type tools described elsewhere. In a vertical well, the length of the producing interval may not be that great. However, in a horizontal well, one of the purposes of making the section horizontal is to open up the interval to a long length. Under these conditions, the positioning of the completion string begins to play a large role in the effectiveness of the production as well as possibly how long it will last.
Knowledge of the size, shape, and orientation of the wellbore are an essential part in being able to predict what might happen downhole as the completion string is inserted into the wellbore.